Reductions in phytoplankton numbers and biomass also limit food to fish larvae and other consumers further up the food chain (Birnbaum 2006). An individual zebra mussel can filter one to two liters of water each day as a result high densities of zebra may cause major shifts in the plankton communities of lakes and rivers. 2002)Įcosystem Change: Most of the impacts of zebra mussels in freshwater systems are a direct result of their functioning as ecosystem engineers (Karayayev, et al. 1994a Sinitsyna & Protasov 1994, in Karayayev et al. Once introduced, populations of zebra mussel can grow rapidly and the total biomass of a population can exceed 10 times that of all other native benthic invertebrates (Sokolova et al. polymorpha has been the most aggressive freshwater invader worldwide (Karayayev et al. The information in this document is summarised below. Zebra mussel are most abundant in hard waters (30-50 mg Ca L-1) but occur in water with Ca concentrations as low as 12 mg Ca L-1 (Cohen and Weinstein 2001).įor a detailed account of the environmental impacts of Dreissena polymorpha please read: Dreissena polymorpha Impacts Information. They are able to tolerate low oxygen content in water for several days and to survive out of water under cool damp conditions for up to three weeks (DAISIE 2006). Zebra mussels prefer moderately productive (mesotrophic) temperate water bodies and occur from the lower shore to depths of 12 m in brackish parts of seas and to 60 m in lakes (DAISIE 2006). They are, however, extremely sensitive to rapid fluctuations in salinity in the northern Gulf of Mexico, where tidal fluctuations are not great, zebra mussels are found to invade areas with salinities up to 12 ppt, however, they appear unable to tolerate salinities above 12 ppt for any extended period (GSMFC 2005). They tolerate brackish waters with salinity up to 7 ppt (DAISIE 2006). Zebra mussels tolerate temperatures from -20☌ to 40☌ the best growth is observed at 18-20☌ (DAISIE 2006). In their occupied invaded range they will colonise similar habitats with the most typical habitats colonised being lakes, rivers, and estuaries, particularly places where there are firm surfaces suitable for attachment (DAISIE 2006). \r\nIn their native region zebra mussels will colonise surface standing waters, surface running waters, the littoral zone of inland surface waterbodies, estuaries, brackish coastal lagoons, large estuaries and inland waters, and hard and soft bottom habitats (DAISIE 2006). Populations on plants also were dominated by mussels less than a year old, as compared with benthic populations as the mussel colonies grow they sink the macrophytes to which they are attached. Within Polish lakes, perennial plants maintained larger populations than did annuals (Stanczykowska & Lewandowski 1993, in Benson & Raikow 2008). Long-term stability of substrate affects population density and age distributions on those substrates. As adults, they have a difficult time staying attached when water velocities exceed two meters per second (Benson & Raikow 2008). Zebra mussels attach to any stable substrate in the water column or benthos including rock, macrophytes, artificial surfaces (cement, steel, rope, etc.), crayfish, unionid clams and each other, forming dense colonies called druses (Benson & Raikow 2008). Given a choice of hard substrates, zebra mussels do not show a preference. In areas where hard substrates are lacking, such as a mud or sand, zebra mussels cluster on any hard surface available (Benson & Raikow 2008). Although the juveniles prefer a hard or rocky substrate, they have been known to attach to vegetation (Benson & Raikow 2008). Zebra mussel larvae are planktonic for 2-4 weeks, prior to beginning their juvenile phase by attaching themselves to substrates by means of byssal threads. Adult mussels can voluntarily detach and move around the substrate to seek alternate locations. polymorpha is variable, but can range from 3 to 9 years (Benson & Raikow 2008). They may mature within the first year of life under optimal conditions maturity in the second year is more usual. They then attach themselves to substrates by means of a byssus, a cluster of threads produced by an external organ near their foot (Benson & Raikow 2008). The larvae develop into their juvenile stage once they have reached about 350 microns in size by settling to the bottom where they crawl about by means of a foot, searching for suitable substratum (Benson & Raikow 2008). Larvae normally disperse by being passively carried downstream with water flow (Benson & Raikow 2008). Optimal temperature for larval development is 20 to 22oC (Benson & Raikow 2008). Veligers develop from a d-shaped to umbonal morphology, and remain planktonic for up to 4 weeks. Fertilised eggs hatch into trocophores (40-60 microns, 1 to 2 days), which develop within a day into a free-swimming planktonic veliger.
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